Memory metal plug

ABSTRACT

Memory metal plugs adapted to seal tubes are formed with a central post and laterally extended disks or rings. The plugs are formed from memory metal that is machined and heat treated to establish favorable temperature profile for the memory metal. The plugs are deformed in an apparatus that holds the plugs and cools the plugs to transform them into the martensitic state. A ram is used to force the cooled plugs through a die to decrease their diameter. These plugs can then be inserted into a tube and heated, causing them to return to their original state and thereby plug the tube.

RELATED APPLICATION

This application is a regular utility application of U.S. ProvisionalPatent Application Ser. No. 60/741,621, filed on Dec. 2, 2005, theentire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Frequently, it is necessary to plug or seal a tube or circular opening.Plugs can be used to seal bores formed in diesel engines, such as theplug disclosed in U.S. Pat. No. 6,053,992. Plugs are also used to sealtubes in heat exchangers. There are a wide variety of different methodsused to seal such devices, none of which are totally satisfactory. Incertain applications, explosive devices are used to seal off a tube.But, this is very expensive. Mechanical devices can also be used; but,in high pressure applications, these may fail.

A potentially useful plug to seal tubes is disclosed in Hall U.S. Pat.No. 5,189,789. This discloses the use of a memory metal or Nitinol plug.Memory metals are alloys that undergo a reversible transformation froman austenitic state to a martensitic state with changes in temperatures.At colder temperatures, the alloy enters the martensitic state andreverts to the austenitic state at higher temperatures. A plug in themartensitic state can be bent or shaped. When the metal reverts to theaustenitic state it reverts to its original shape.

The plug disclosed in Hall U.S. Pat. No. 5,189,789 is formed from such amemory metal and includes a central post with a plurality of disks thatextend perpendicular to the post. The disclosed plug is placed in a bathof methanol and dry ice to cause it to enter the martensitic state. Itis then forced through a die which bends or swages the disks, decreasingthe exterior diameter of the plug. The plug can then be manually placeinto a tube and heated, causing it to revert to the austenitic state atwhich point in time it will bend back to its original shape, increasingits diameter and, thus, plugging the tube. These plugs are preferablyformed from Nitinol, which is an alloy of nickel and titanium.

Unfortunately, the plug disclosed in the Hall reference tends to breakwhen swaged. The design of the plug as well as the disclosed method ofswaging the plug produced very unreliable results.

SUMMARY OF THE INVENTION

The present invention is based on the realization that an apparatus canbe utilized that supports the unswaged memory metal plug in a holder andchills it while it is in the holder to transform it to the martensiticstate. Preferably, the plug is chilled using liquid carbon dioxide orother cryogenic fluids at temperatures below the lower martensitictransition temperature of the memory metal alloy. Preferably, the plugis placed in a die and coolant is forced through the die walls onto theplug. The plug, while in the holder, can then be forced by a ram througha die to swage it, allowing it to be used.

This ensures that the plug is cooled adequately. A thermocouple can alsobe used to measure the plug temperature and prevent the ram fromactivating before the plug reaches the martensitic state.

The plug is designed with radiused regions between the disks and centralrod which further prevents breakage.

The deformed plug connected to a heat conducting holder is inserted intoa tube. The holder and plug are heated, causing the plug to revert tothe austenitic state and into its original configuration, thus expandingand sealing the tube.

The objects and advantages of the present invention will be furtherappreciated in light of the following detailed description and drawings,in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a plug for use in the present invention;

FIG. 2 is a plan view of a plug and holder assembly for use in thepresent invention in its austenitic state;

FIG. 3 is a plan view of a plug and holder assembly for use in thepresent invention in its deformed martensitic state;

FIG. 4 is a diagrammatic depiction of the insertion of the plug of thepresent invention into a tube.

FIG. 5A is a cross sectional view of the apparatus used in the presentinvention showing the plug above the die.

FIG. 5B is a cross sectional view of the apparatus shown in FIG. 5A withthe plug in the upper portion of the die.

FIG. 6 is a diagrammatic depiction of the operation of the presentinvention.

FIG. 7A is cross sectional view of a Nitinol plug inserted into a tubein the swaged condition, as shown in FIG. 3.

FIG. 7B is a cross sectional view of a Nitinol plug inserted into a tubein its austenitic unswaged configuration.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the present invention utilizes a plug 10 thatincludes a central axial post 12 and first, second and third circulardisk-shaped flanges 14,16, and 18, generally referred to as disks. Theplug 10 is shown with three disks but can be made with as few as one andas many as desired. Two or more disks are preferred because multipledisks help align the plug in use. Each of the first, second and thirddisks have first and second surfaces 13 a and 13 b. At the juncturesbetween the surfaces and post 12 are radiused portions 15. The radiusedportions can be located at any of the junctures between the posts andthe disks. Preferably, they are at the juncture of the first surface 13a of the first disk 14 and at the junctures between the post 12 and thefirst and second surfaces 13 a, 13 b of the second 16 and third 18disks.

Each of these radiuses should be greater than 0.003 inch, morepreferably greater than 0.015 inch, and, in a preferred embodiment, isgreater than about 0.03 inch. As shown, they are a complete radius ofabout 0.093. These radiused portions provide stress relief in both thedeformation of the plug 10, and during use of the plug 10. This allowsthe plug to be deformed more, thus further reducing the diameter of thedeformed plug.

Generally, for a plug having a diameter of 1 inch, the post 12 will havea diameter of 0.10 to 0.3 and the disks will be 0.05 to 0.25 inch thick.For a 0.5 to 1 inch diameter plug, a thickness of 0.187 functions well.

Plug 10 is formed from a memory metal alloy. As discussed below, it isimportant to select a memory metal alloy that has an appropriatetemperature profile so that the conversions between the martensiticstate and austenitic state are accomplished at temperatures that makethe plug 10 commercially useful. Preferably, the memory metal isNitinol. Such memory metals can be purchased. One supplier of suchmaterials is Special Metals, Shape Memory Alloy Division, located in NewHartford, N.Y. A preferred material is one with 50 mole percent nickeland 50 mole percent titanium.

Preferably, plug 10 is machined from Nitinol which converts to themartensitic state at about 0° F., and remains in the martensitic stateuntil heated to a temperature of about 95° F., or higher. Such materialis generally purchased as bar stock or rod stock, and must be furthermachined in its austenitic state to provide a plug 10, as shown inFIG. 1. In order to form such a plug, a rod of the material having thedesired cross sectional dimension is machined using, for example, a CNClathe screw machine or grinder to provide the plug 10 with center post12 and a plurality of disks 14, 16 and 18 (as shown). The peripheraledges of these disks are radiused to facilitate swaging. The trailingperipheral edges are not radiused. This provides a better seal in use.

During the machining of these plugs 10 the temperature profile may bemodified. Accordingly, after machining, the plugs 10 are subjected to aheat treatment to restore the shape memory response of the alloy.Preferably, subsequent to machining, the plug 10 is heated to atemperature of about 900° F. for a period of 30 minutes.

The plug 10, as shown in FIG. 1, is swaged or deformed utilizing anapparatus 30, shown in FIGS. 5A and 5B. The apparatus 30 includes acentral housing 32 that has an upper opening covered with cover 34. Adie 38 is located within housing 32. Cylindrical metal die 38 issupported in a cylindrical support 46 which in turn is supported on aledge 48 in housing 32. The support 46 includes an annular outer passage41 which communicates between cryogenic inlets 42 and 44. This outerannular passage 41 communicates with a series of holes 45 which aredirected to an inner annular passage 47 which surrounds die 38. Die 38is in turn supported on a ledge 48 of support 46 and includes a seriesof holes 49 that align with the inner annular passageway 41 of thesupport 46. A thermocouple 50 is located on ledge 48 in contact with die38 to measure the temperature of the die.

The die 38 includes an upper portion 52 and a lower portion 54. Theupper portion 52 includes a cylindrical passage that is not tapered andadapted to receive the unswaged plug 10 as shown in FIG. 5A. The lowerportion 56 of die 38 is tapered so that the bottom opening has adiameter equal to the desired diameter of the swaged plug. Cover 34located above container 32 includes a central opening 56 aligned withthe ram 58 of press 60 as well as the central axis of die 38.

The bottom 62 of housing 32 includes a channel 64. A cup 66 with a rim68 attaches to the lower portion 62 of housing 32 with the rim 68located in channel 64. Cup 66 is aligned directly beneath the die 38.

Exterior of housing 32 is a frame 65 with two side frame members 72 and74 and a horizontal upper frame member 80. Press 60 is supported onupper surface 80.

As shown in FIG. 5A, an unbent Nitinol plug 10 (which is in theaustenitic state) is positioned above die 38. The central opening of theupper portion of die 38 is slightly smaller than the outer diameter ofplug 10. A holding rod 84 having a central bore at a first end 86 isplaced on the post 12 of plug 10, centered with the opening throughcover 34. The second end 88 of the holding rod 84 has a conical shape.An extension rod 90 is placed through the opening in cover 34. This hasa first end 92 adapted to be engaged with the ram 58 from the press 60and a second end 94 having a conical recess adapted to engage the secondend 88 of holding rod 84.

FIGS. 5A, 5B, and 6 combine to show a diagrammatic depiction of theoperation of the present invention. With the plug 10 in position asshown in FIG. 5A and a safety shield (not shown) in place, switch 100 isactivated which causes the first portion 102 of press 60 to force ram 58down a predetermined distance which causes the extension 90 to engagethe holding rod 84 and force the plug 10 into the upper untaperedportion 52 of die 38. This is shown in FIG. 5B. Switch 100 also causescryogenic fluid to be forced through inlets 42 and 44 through theannular passage 41 through passages 45 in the holder to the innerannular passage 47 and, subsequently, through the passages 49 in the die38 chilling the plug 10. Thermocouple 50 measures the temperature of thedie 38 and, in turn, the plug 10. When this temperature reaches apredetermined set temperature, generally about −50° F., the secondportion 106 of press 60 is automatically activated, which forces the ram58 further, as indicated by arrow 108, forcing the plug 10 with theholder 84 through the die 38 into cup 66, as indicated by arrow 110. Thetapered lower portion of die 38 bends the discs 14, 16 and 18, leavingthe plug 10 in the configuration shown in FIG. 3. Thus, the swaged plug10, shown in phantom in FIG. 5B, will be collected in cup 56.

The die 38 is configured to bend the disks 14, 16, 18 between 10 and 25degrees from their originally perpendicular relation to post 12 so thatthe effective plug diameter is decreased 2-5% for plugs with a nominaldiameter of 0.5 to 1 inch. In the embodiment shown in FIGS. 5A and 5B,the entry diameter of die 38 is 0.703 inch and the exit diameter is0.688 inch corresponding to a disk bending of 15° for a plug having anominal 0.187-inch diameter central post.

To use the plug to seal a tube, the plug 10, in the deformed state,i.e., martensitic state, as shown in FIG. 3, is inserted into a tube 111as shown in FIG. 7A in the direction of arrow 112. Holding rod 84isattached to post 12 to facilitate this. As shown in FIG. 4, the plug 10can be inserted anywhere in tube 111, including at the tube plate 113,as shown by plug 10(a). The deformed plug should be of a size whereinthe outer diameter of the deformed plug is about 0.03 inches less thanthe inner diameter of the tube.

Once inserted into the tube with the holder 84 still in position, theplug is heated to a temperature effective to cause the plug to convertto the austenitic state. This should not exceed 550° F. The heating canbe the result of residual heat in the tube or an external heat sourcesuch as a blow torch. Holder 84 is a thermally conducting metal such assteel. Therefore, it facilitates heating the plug 10. When thetemperature of the plug reaches the transition temperature to theaustenitic state, the plug 10 reverts to its original condition,increasing its diameter and, in turn, pressing against the side walls oftube 111 as shown in FIG. 7B.

Once in position with the plug 10 back in the austenitic state andsealing the tube 111, the holder 84 can be pulled from the plug. Thefriction fit between the holding rod 84 and post 12 allows one to removethe holder 84 using a pair of pliers.

The compression fit between the expanded plug 10 and the inner wall oftube 111 as shown in FIG. 7B is sufficient with at least 0.004″interference to withstand a pressure of about 6,000 psi. Thus, this willwithstand repeated heating and cooling cycles remaining securely inplace, providing a reliable seal. This, in turn, allows a heat exchangetube which has a leak to be sealed off quickly and reliably, allowingthe heat exchanger to be put back into operation quickly andinexpensively.

This has been a description of the present invention along with thepreferred method of practicing the present invention. However, theinvention itself should only be defined by the appended claims, WHEREINWE CLAIM:

1. A method of swaging a memory metal plug, said plug having at leastone laterally extended disk comprising positioning said plug in contactwith a die aligned with an opening in said die; spraying a coolant ontosaid plug to convert said plug from an austenitic state to a martensiticstate, forcing said plug through said die to deform said disks therebydecreasing the diameter of said plug.
 2. The method claimed in claim 1wherein said refrigerant is carbon dioxide.
 3. The method claimed inclaim 2 wherein said plug is held in a housing and a spacer is placed onsaid plug, and wherein said plug is forced through said die by forcingsaid spacer downwardly through said die.
 4. The method claimed in claim1 wherein said plug is held in said die and said refrigerant is sprayedthrough said die onto said plug.
 5. The method claimed in claim 4further comprising measuring the temperature of said die to determinethe temperature of said plug and forcing said plug through said die whena predetermined temperature of said die is detected.
 6. An apparatus toswage a memory alloy plug, said plug having a plurality of laterallyextended disks comprising an annular die having an inlet opening, anupper untapered portion, and a lower tapered portion; said upper portionadapted to support said memory metal plug; a plurality of coolant inletsthrough said upper portion of said die; and a ram adapted to force saidplug from said upper portion of said die through said die.
 7. Theapparatus claimed in claim 6 wherein said coolant inlet comprises aplurality of orifices.
 8. The apparatus claimed in claim 6 furthercomprising a thermocouple associated with said die said thermocoupleassociated with a second switch which controls aid ram.
 9. The apparatusclaimed in claim 7 comprising a first switch adapted to activate saidram to force said plug into an upper portion of said die and said secondswitch adapted to activate said ram to force said plug completelythrough said die.
 10. The apparatus claimed in claim 8 furthercomprising a container adapted to catch a plug that has been forcedthrough said die.
 11. The apparatus claimed in claim 7 furthercomprising means to set a temperature where said second switch isactivated by means of said thermocouple detecting said temperature. 12.A memory metal plug having a central post and at least one disk extendedradially outward from said post, a radiused portion between a junctureof said post and said disk extended around said post.
 13. The plugclaimed in claim 12 wherein said plug has a plurality of disks.
 14. Theplug claimed in claim 13 wherein each disk includes a first and secondsurface and wherein said radiused portion is at a juncture of said postand said first surface.
 15. The plug claimed in claim 13 having a firstdisk and a second disk, said post extended from said first disk throughsaid second disk, and wherein said radiused portion is at a junction ofsaid rod and said second surface of said second disk.
 16. The plugclaimed in claim 12 having first, second and third disks, each diskhaving first and second surfaces, said plug having radiused portions atthe junctures of said post and said first surface of said first disk,and at the junctures of said post and said first and second surfaces ofsaid second disk.
 17. The plug claimed in claim 12 wherein said radiusedportion has a radium greater than about 0.015 inches.
 18. The plugclaimed in claim 17 wherein said radius is at least about 0.03 inches.19. A memory metal plug comprising a central post and at least one disk,said post having a tip extended out from a surface of said disk, ametallic heat conducting rod compression fitted to said tip.
 20. Theplug claimed in claim 19 wherein said metal rod is steel.